This invention relates to an apparatus for printing both sides of a web of paper or like printable material, and particularly to such a double-side printing apparatus employing an ink-jet printer or printers for printing each side of the web.
Ink-jet printers by reason of their very construction presuppose use with their printing heads oriented downwardly. This operational requirement peculiar to ink-jet printers has imposed limitations upon their arrangement in use for printing both sides of a web. The opposite sides of the web are not printable concurrently, but only one after the other.
Japanese Unexamined Patent Publication No. 8-216467 suggests an arrangement in which a set of, for example, four ink-jet printers are aligned in the traveling direction of the web, and another such set in side-by-side relation to the first recited set. All the printers have their printing heads oriented downwardly. The web is first guided past the first set of printers to have one side thereof printed, and then turned aside and back past the second set of printers to have the other side printed. This conventional side-by-side arrangement of the two sets of ink-jet printers offers the advantage of reduction in the dimension of the apparatus in the traveling direction of the web from the supply station to the delivery station.
Offsetting this advantage of the prior art is the use of turning bars for turning aside and reversing the web from one set of ink-jet printers to the other. The web when traveling over the turning bars is particularly prone to the frictional development of static electricity, as well as lateral displacement or meandering. Another problem is that, arranged side by side, the two sets of ink-jet printers adds to the transverse, or one horizontal, dimension of the apparatus. The greater transverse, rather than vertical, dimension is undesirable because it is tantamount to a greater floor space requirement of the apparatus.
The object of the present invention is, in a double-side printing apparatus of the kind defined, to eliminate turning bars. Thus, parallel guide rollers only are used to guide the web from one printing means, such as an ink-jet printer or set of such printers, to another.
Another object of the invention is to reduce the lateral dimension, and therefore floor space requirement, of the doubleside printing apparatus to a minimum.
Still another object of the invention is to dry the printings on the web surfaces immediately after they have been made, with the drying means compactly arranged so as not to add to the floor space requirement of the apparatus.
Summarized in its perhaps broadest aspect, the invention concerns a double-side printing apparatus comprising a first printing mechanism for printing one side of the web, and a second printing mechanism for printing the other side of the web. The first and the second printing mechanisms are spaced from, and in register with, each other in a prescribed direction. Also included are guides for guiding the web past the first and the second printing mechanisms one after the other.
In the preferred embodiment of the present invention, the first and the second printing mechanisms each take the form of a series of ink-jet printers. Both series of ink-jet printers extend horizontally, with a vertical spacing therebetween, and with their printing heads all directed downwardly. The web is first threaded in a forward direction (i.e. from infeed toward delivery) past one series of ink-jet printers, then reversed to travel backwardly past the other series of ink-jet printers, and then reversed again to travel toward the delivery.
Thus, the web can have its opposite sides printed while traveling along a path that is contained in one vertical plane. No turning bars are needed, and only parallel rollers suffice, for threading the web past the two vertically-spaced series of printers. The web therefore does not produce static electricity by frictionally traveling over turning bars, and thus does not attract the fine dust particles that invariably fill the printing plant air.
Furthermore, as the two series of ink-jet printers are arranged one over the other, the apparatus according to the invention is materially reduced in lateral dimension compared with the prior art in which the two series were in side-by-side arrangement. Although somewhat increased in height, a factor that causes little or no inconvenience, the apparatus according to the invention gains a far more pronounced advantage of occupying significantly less floor area.
The dispensation with turning bars, made possible by this invention, leads to a simpler, more streamlined path of the web. As a consequence, not only is the apparatus simplified in construction, but the images printed by the respective ink-jet printers are bound to achieve a higher degree of registration.
A further feature of the invention resides in a device for drying the printings made on both sides of the web. In the preferred embodiment, the drying device takes the form of drums around which the web is guided. Each drum is arranged downstream of one series of ink-jet printers, and both drums are inconspicuously positioned in only one drier zone located under the two series of ink-jet printers. The drum driers are also well calculated to keep the space requirement of the apparatus at a minimum.
The above and other objects, features and advantages of this invention will become more apparent, and the invention itself will best be understood, from a study of the following description and appended claims, with reference to the attached drawings showing the preferred embodiment of the invention.